The present invention relates to a development apparatus for an electrostatic image formation and, more particularly, to a development apparatus which uses a liquid developer.
A conventional apparatus for developing a latent electrostatic image on a photoconductive drum by means of a liquid toner has been proposed in U.S. Pat. No. 4,202,620. In the proposed apparatus, the liquid toner is located close to but out of contact with a latent image carrier, i.e., the photoconductive drum, so that the background where the latent image is not formed becomes less smudgy and less smeary. U.S. Pat. No. 4,202,620 disclosed a toner supplier device provided with a capillary passageway for supplying toner formed between two plates which are opposed to each other with a small clearance. When the device is submerged at one end thereof in a liquid toner, the liquid toner advances to the other end of the device due to capillarity to thereby form meniscus. The device is supported in such a manner that its longitudinal direction is parallel to the rotary shaft of the photoconductive drum, and that the meniscus is held close to, but out of contact with, the surface of the photoconductive drum.
When the latent electrostatic image formed on the photoconductive drum approaches the other end of the toner supplier device or the meniscus of the liquid toner with the movement of the photoconductive drum, a projection grows from a surface of the liquid toner toward the photoconductive drum to eventually come in contact and adhere only on the latent electrostatic image owing to electrostatic field. Since the device can use an aqueous toner as the liquid toner, undesirable organic vapor will not be generated from solvent when the liquid toner is dried.
However, the conventional development apparatus is not completely free of drawbacks as the liquid toner tends to be supplied in excess from the supplier device to the photoconductive drum. As the projection starts to form, the electrostatic field of the latent electrostatic image tends to concentrate on that portion. Therefore, if a plurality of fine picture elements of the latent image exist close to each other, only one projection which is initially formed grows to reach the latent image, rather than the plurality of projections being formed to correspond to respective picture elements of the image. As a result, a fine latent image cannot be developed clearly.
The above-mentioned development apparatus has a further shortcoming that, when the apparatus is inclined or applied with impact, the liquid toner tends to flow over from the other end of the supplier device filling in a gap between the photoconductive drum surface and the toner supplier device due to the surface tension of the liquid toner, to thereby incapacitate the proper development operation. Moreover, the liquid toner easily spills within the apparatus to contaminate it.